Political Polarization and Policy Expertise: Theory and Evidence from State Supreme Courts

Tinghua Yu (London School of Economics and Political Science)
Elliott Ash (ETH Zurich)
Bentley MacLeod (Columbia University)

Abstract: We provide theory and evidence on how political polarization at the mass level affects politicians' policy decisions in common value issues. In the model, politicians representing two groups of voters with divergent ideologies compete for office. Voters have limited information about policy as well as politicians' competence in policy making. After observing the incumbent's policy choice, voters make voting decisions. We study two variations of election. First, there is a majority group and a minority group in the society. Second, society is composed of two competitive groups. In both variations, we show that in a society with a high level of polarization, the incumbent politician is more likely to exercise her expertise regarding common value issues. We take these predictions to data in the context of state supreme courts. We find that under partisan elections, judges who joined the court when polarization was high write higher-quality decisions (receiving more citations from other judges) than judges who joined when polarization was low.